A suitable hubless Alexa Switch had been sitting under our noses for a few weeks.
It is called the “Virtual Lock” which can be easily created using the Simple Device Viewer or the beta API Browser+.
The lock can be manually operated in the ST App, and/or it can be controlled by ST Routines. On the Alexa side it can be used as a trigger in Alexa routines.
Two minor problem are the Lock Icon and it says locked/unlocked vs on/off which can’t be changed.